Dendritic spines of neurons are micron-sized, post-synaptic structures. Along with dendritic arbors and axons, they form the complex neuronal circuits of our brains. Rho GTPases, in particular Rac, have long been implicated in regulating the formation and remodeling of these structures. Thus it is not surprising that genetic alteration or pharmacological perturbation of Rac signaling can have a profound impact on dendritic development and synaptic function. While its importance is well recognized, our understanding of Rac regulation in neurons remains at the level of bulk biochemistry. Few studies have been able to directly demonstrate the spatial and temporal regulation of Rac activation in dendrites and spines. Here we propose to develop enabling imaging technologies that are tailored for visualizing and manipulating signaling in minute spaces such as dendrites and dendritic spines of neurons.